1 Field of the Invention
The present invention relates to a method of operation of a navigational calculator and, in particular, to the method by which a navigational calculator interfaces with a user by its input and output devices.
2. Description of the Related Art
Presently, there are several different types of navigation calculators available. A common characteristic of substantially all navigational calculators is that they each possess an input device that allows a user to communicate with the navigational calculator and an output device that allows the calculator to communicate with the user. Typically, the input device is a keyboard and the output device is a display screen, such as a CRT, LED, or LCD.
An important feature that distinguishes several of these different types of navigational calculators from one another is the method in which the user and the calculator communicate via the input and output devices in the course of computing a navigational parameter. One general approach that is employed by several navigational calculators requires the user to enter the value of a variable that is necessary to the calculation of a particular navigational parameter into the calculator using a keyboard and, either before or after entry of the value, identify the variable with which the value is associated using the keyboard. Once the user has entered the values for all of the variables necessary to calculate the desired navigational parameter, the user causes the navigational calculator to compute the desired navigational parameter by actuating the appropriate key on the keyboard. An example of a navigational calculator that implements this method is discussed in U.S. Pat. No. 4,156,912. A drawback of the method is that the user must know all of the variables that need to be defined in order to calculate a particular navigational parameter. This can be overwhelming in navigational calculators that are capable of computing more than a few navigational parameters or where a particular navigational parameter requires that the values of a substantial number of variables be defined. Consequently, this method is typically used with navigational calculators that compute a relatively small number of navigational parameters. Such a navigational computer is discussed in U.S. Pat. No. 4,236,212.
Another method that is used to transfer information between a user and a navigational calculator via the calculator's input and output devices requires the user to select, at the outset of the computation, the navigational parameter that is to be calculated using the input device. Once the user has selected a navigational parameter, the calculator then prompts the user to enter the values of the variables necessary to compute the selected navigational parameter in a predetermined order or sequence that is dictated by the navigational calculator. An example of this method is discussed in U.S. Pat. No. 3,979,057. One drawback associated with this method is that the user is required to define the values of the variables in a defined sequence. This can be quite inconvenient if, for example, the pilot of an aircraft must look at a piece of instrumentation on one side of the cockpit to obtain the value of one variable, then look at an instrument on the other side of the cockpit in order to obtain the value for the next variable in the sequence, and then look back again to the other side of the cockpit for the next variable in the sequence.
Another drawback typically associated with navigational calculators where the user is required to enter data in a particular order is that once a value for a variable is fixed or defined it often cannot be changed without starting the entire navigational computation process over. Obviously, this can be quite burdensome if the calculation of a particular navigational parameter requires that the values of several variables be defined.
Yet another disadvantage that is associated with the manner in which the method of initially selecting a navigational parameter and then subsequently entering data in a defined sequence is typically implemented is that, following the selection of the navigational parameter that is to be calculated, the navigational calculator displays the values of the variables necessary to calculate the selected navigational parameter from the last calculation in which the values of the variables were provided or determined. This disadvantage may also be present in navigational calculators that implement the initially discussed method where the user initially enters the values of variables and subsequently identifies the navigational parameter that is to be calculated using the values of the variables previously entered. If, as typically happens, the user is momentarily distracted when entering the value of a particular variable, then the old value for the variable may be entered by the user and result in the calculator computing an erroneous value for the selected navigational parameter that, if detected, will necessitate that the calculation be repeated.
Another undesirable feature that may be associated with practicing the method of initially selecting a navigational parameter and then subsequently entering data in a defined sequence is that in navigational calculators where a multi-line display is used, such as the one discussed in U.S. Pat. No. 4,831,538 ('538), is that, following the selection of the navigational parameter that is to be computed, the calculator displays the selected navigational parameter together with the last value calculated for the navigational parameter and continues to display this value while the user enters the required data to make the calculation. This is typically quite confusing because a user may not realize that the value of the selected parameter being displayed is from a previous calculation and, instead, believe that the displayed value is based upon the values of the variables that the user has entered.
A further disadvantage that is typically associated with navigational calculators that implement the method of initially selecting a navigational parameter and then entering data in a defined sequence where a navigational calculator with a multi-line display is used is that variables other than those required to calculate the selected navigational parameter are displayed. This, too, can be quite confusing to the user of a flight calculator.
The navigational calculator disclosed in the '538 appears, as many of the other presently known navigational calculators, to allow the user to change the value of a variable used in the calculation of a navigational parameter to determine the effect of the change in value of the variable on the value of the navigational parameter. For instance, a navigational calculator may have determined the distance an airplane would travel based upon the ground speed and time of flight information provided by the user. The user may then wish to determine how much further the airplane would travel based on the same ground speed but a greater amount of time than was initially used. Navigational calculators, such as that discussed in the '538 patent, appear to allow the user to change the time of flight and then recompute the distance that would be traveled based on the ground speed used in the initial calculation and the new time of flight. While this is a desirable feature in many situations, it is inefficient in situations where the user wishes to determine the effect of changing the value of a previously calculated navigational parameter on one of the variables used to calculate the navigational parameter. For example, if the user wanted to determine the time of flight necessary to cover a distance different than that in the initial calculation using the same ground speed that was used in the initial calculation, the user would have to make a guess on the time of flight that would, based on the ground speed used in the initial calculation, result in the required distance. The user would then have to provide the calculator with this guess at the new value of the time of flight variable and have the navigational calculator recalculate the distance parameter. This process of guessing at the value of a flight variable that will result in the required distance being computed by the navigational calculator, entering the value into the navigational calculator, and recomputing the distance parameter continues until the navigational calculator computes the required desired distance or a distance that is close enough to the desired distance for the user's purposes. Obviously, this is a very time consuming and inefficient process.
Based on the foregoing, there is a need for a method of transferring information between a navigational calculator and a user via the input and output devices of the calculator that is more convenient and reliable than the methods employed in presently known navigational calculators. More specifically, there is a need for a navigational calculator where the user is not required to define the values of the variables required to compute a particular navigational parameter in a defined sequence. Additionally, a method for communicating information between a navigational calculator and a user is needed that allows the user to change the value of a variable that has been defined without having to redefine the values associated with other variables involved in the calculation of the navigational parameter. Additionally, there is a need for a method of transferring information between a navigational calculator and a user where the user is less susceptible to being mislead by having values from previous calculations being associated with the variables or selected navigational parameter of a current calculation. Moreover, there is a need for a method of operation of a navigational calculator where, for a desired navigational parameter calculation, only those variables that are necessary for carrying out the calculation are displayed on a multi-line output device. In addition, there is a need for a navigational calculator where the user is provided with information on the effect of changing the value of a previously calculated navigational parameter on the value of a variable used in the initial calculation of the navigational parameter.